The presence of corrosive products, contaminants, metallic particles, oxidation, etc. in fluids, such as lubricants, can cause problems. For example, contaminants in lubricants can lead to damage of machinery in which the lubricant is utilized, causing unnecessary or accelerated wear on the lubricated members.
Various approaches have been developed to detect conditions involving deterioration and/or contaminants in fluids. One conventional system described in U.S. Pat. No. 4,646,070 utilizes a pair of capacitor electrodes positioned in a fluid. The fluid serves as a dielectric between the electrodes to develop a frequency voltage signal across the capacitor electrodes. Based on such signal, the dielectric, and therefore, the deterioration of the fluid is determined. However, this solution suffers from a drawback in that the sensor is large and bulky and is difficult to move from machine to machine to make fluid contamination measurements.
U.S. Pat. No. 5,262,732 describes a system, which utilizes an oscillator circuit coupled to a capacitive sensor. The fluid under test is placed in a reservoir containing the capacitive sensor. The oscillator circuit generates a signal having a frequency that increases or decreases depending on the capacitance of the sensor. The system of U.S. Pat. No. 5,262,732 is also rather large and cumbersome and does not lend itself to portability. In the field, it would be difficult to transport the device from machine to machine to analyze the lubricant at the location of the machinery, for example.
Some prior art sensors have been rather large so that a user could insert the sensor into the fluid and thereby remove a fluid sample from a machine for analysis. This large, sturdy construction also allowed the sensor to be subsequently cleaned for use at another machine without causing damage to the sensor. Unfortunately, in some machines, obtaining a manual fluid sample with a large, unwieldy sensor is inconvenient due to machine construction. Also, in some applications, it is desirable to affix a lubricant analysis sensor to the machine in the lubricant fluid flow path (called an in-line configuration) in order that a user may merely attend the machine and obtain a lubricant contamination reading without having to insert an analyzer apparatus into the fluid flow path. In some cases, prior art sensors are too large and unwieldy and do not conveniently affix to the machine without interfering with proper machine operation.
As disclosed in U.S. Pat. Nos. 4,047,814 and 5,504,573, magnetic field gradients have been utilized to precipitate conductive or ferromagnetic particulates out of a sample fluid (e.g., a lubricant) such that particulates of varying sizes are withdrawn along a horizontal strip for subsequent analysis. Knowledge of the particulate size distribution is then utilized to determine the status of machinery wear and the potential for failures from wearing parts, etc. Prior to U.S. Pat. Nos. 4,047,814 and 5,504,573, this method relied upon a visual analysis of particulate distribution, which was a strong function of the technician's experience performing the analysis, thereby leading to inconsistent conclusions. In addition, since the horizontal strip was removed for analysis, evaluation of the fluid at the machine site was difficult and, in many cases, impossible.
U.S. Pat. Nos. 4,047,814 and 5,504,573 provided analysis improvement over the manual analysis by illuminating the particulate distribution with radiation and detecting the radiation via a plurality of photodetectors that traverse the particulate sample. Although such a technique provides for an improvement in subsequent analysis conclusions, this technique does not overcome the requirement that an operator initially procure the sample and send it off-site for analysis. The sample must still be removed for analysis which limits the locations in which such analysis materials may be located and, in some cases, prohibits their use altogether. Further, if one wishes to affix the particulate distribution collection apparatus with its analysis equipment so that the horizontal strip need not be removed from the machine, the radiation source and photodetectors are undesirably large and thereby further limit the scope of their application.
A miniature sensor for lubricant analysis was disclosed in commonly owned U.S. Pat. No. 6,204,656. The sensor included one or more micro-miniature sensors that provided a substantial reduction in sensor dimensions relative to prior art sensors. The sensors are incorporated into probes for easy lubricant fluid accessibility or in an in-line configuration. The sensors sense a capacitance of the fluid (therefore the impedance), and based on the impedance, determine the condition of the fluid. The sensor disclosed in U.S. Pat. No. 6,204,656, however, determined the impedance of the fluid based on the magnitude of the impedance and contaminant selective materials were not thoroughly discussed.
In view of the aforementioned shortcomings associated with existing systems for analyzing conditions of a fluid such as a lubricant, there is a strong need in the art for a fluid screening device which provides detailed information regarding the particular types of contamination, degree of oxidation or other deterioration, etc. Moreover, there is a strong need in the art for such a screening device which is miniature and thereby provides for ease of lubricant contamination status procurement for machine predictive maintenance programs.